Evidence of water spotted on the moon's surface by a sharp-eyed spacecraft likely originated from an unknown source deep in the lunar interior, scientists say.

The find — made by NASA's Moon Mineralogy Mapper instrument aboard India's Chandrayaan-1 probe — marks the first detection of such "magmatic water" from lunar orbit and confirms analyses performed recently on moon rocks brought to Earth by Apollo astronauts four decades ago, researchers said.

"Now that we have detected water that is likely from the interior of the moon, we can start to compare this water with other characteristics of the lunar surface," study lead author Rachel Klima, of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., said in a statement.

"This internal magmatic water also provides clues about the moon's volcanic processes and internal composition, which helps us address questions about how the moon formed, and how magmatic processes changed as it cooled," Klima added.

The Moon Mineralogy Mapper, or M3, imaged a 37-mile-wide (60 kilometers) impact crater near the lunar equator called Bullialdus, whose central peak is composed of a type of rock that forms when magma is trapped deep underground. This rock was excavated and exposed by the impact that formed Bullialdus, Klima said.

"Compared to its surroundings, we found that the central portion of this crater contains a significant amount of hydroxyl — a molecule consisting of one oxygen atom and one hydrogen atom — which is evidence that the rocks in this crater contain water that originated beneath the lunar surface," she said.